This tactical game has far reaching long term implications...
@ "Company A (Microsoft), Company B (Google), Company C (HTC)"
So your question is, why would A go after C, but not B. The simplest literal answer is that B (Google) has much more money and a much higher public profile to be able to effectively fight off A (Microsoft). If Microsoft tried to ask Google to pay up, they know Google would very publicly tell Microsoft to F'off and where to go and jump, because Microsoft can't frighten Google. So the only chess move then open to Microsoft, is to move to take legal action against Google to force them to pay up (or back off in shame proving to the world Microsoft don't really have a case against Linux). So Microsoft know in a legal fight, A vs B is a lot harder to win than A vs C and such a legal battle would generate a huge storm of publicity. It would be so big just about every media outlet in the world would want a ring side seat to watch a Microsoft vs Google battle over Linux. So Microsoft don't want a high profile battle. They want lots of easy quiet victories, which collectively add up to an implied win over Linux.
Microsoft are playing a very tactical game (targeting an audience of non-technical high up powerful people with their *PR battle* against Linux). The Microsoft tactical game is to imply Linux is copying them, rather than *proving* Linux is copying them, because lets face it, if Microsoft had strong grounds to take Linux to court to be able to prove such a direct violation, they would have done it many years ago without hesitation. Therefore Microsoft cannot prove wrong doing, so they are trying to imply wrong doing.
This game has far reaching implications. The first thing Microsoft are achieving with this tactical game is to frighten companies into signing up with Microsoft. That is operating literally like a Protection Racket! ... its bullying people into giving Microsoft money. Thats bad enough, but worse its frightening other companies into complying with Microsoft's bullying tactics as well.
But even worse the more companies they frighten into signing up to the idea Linux needs to license from Microsoft, the nearer Microsoft moves to winning the grand prize of saying to everyone, hey look all these companies say *in writing* they know Linux needs to license from Microsoft, so everyone must now license from Microsoft and sooner or later a non-technical judge will agree with this idea.
After all the law already recognizes the idea that an unprotected idea falls eventually into the public domain. Therefore by constantly *implying* protection is needed against Linux violating Microsoft (as Microsoft are trying to say), then they are trying to prove that they and many companies all agree Linux violates Microsoft. Its a very underhanded attempt to imply wrong doing.
Microsoft know they can't win a direct legal battle against Linux, because they would have tried already if they had a hope in hell of winning. They absolutely would have definitely tried, so its glaringly obvious that they haven't yet tried a direct assault on Linux and haven't tried a direct assault on Google. But make no mistake, sooner or later they will try a direct assault on Linux (and in doing so try to undermine Google), once they have enough frightened companies signed up to say in writing, they all think Linux violates Microsoft.
So Microsoft are playing a very insidious tactical PR battle/game against Linux.